1. Field of the Invention
The present invention relates to an image processing apparatus and a control method thereof.
2. Description of the Related Art
An image processing method, in which a gradation transformation processing (e.g. γ transformation processing) is executed depending on the characteristics of the input image signal, has been available (hereafter, this γ transformation processing is called “dynamic γ processing”). Such a method is disclosed in, for example, Japanese Patent Application Laid-Open Nos. H03-126377, H08-204963 and H06-350873.
In concrete terms, Japanese Patent Application Laid-Open No. H03-126377 discloses a method for creating a cumulative histogram based on a brightness histogram for one frame, and generating a γcurve from the cumulative histogram to perform dynamic γ processing. Japanese Patent Application Laid-Open Nos. H08-204963 and H06-350873 disclose a method for setting the reference values of a dark portion and a light portion based on peak values (frequency values to be a peak value) at a low gradation level side and a high gradation level side in the brightness histogram of the input image signal, and performing dynamic γ processing depending on the reference values being set. Japanese Patent Application Laid-Open No. 2001-125535 discloses a method for performing gradation correction for a gradation level with which the frequency becomes a predetermined upper limit or more, and a gradation level with which the frequency becomes a predetermined lower limit or less in the brightness histogram, using these frequencies as the upper limit and the lower limit respectively.